What happened to Catholic Ireland? The same thing that happened to most other Catholic states in Western Europe: Vatican II. When the Church left the people, and is now oh so surprised that the people responded by leaving the Church.
The epitaph of that disaster will be the one written by John Foxe: “Hodie infusum est venenum in ecclesia Dei”
One of the reasons that Vatican II was called was to address the declining church attendance in Europe after WWII, particularly in France (the eldest daughter of the Church).